It is useful for diagnosing or detecting a disease process to perform a histologic or cytologic examination of a tissue cell sample using a light microscope. This requires that a tissue (cellular material) sample must first be retrieved from the patient, and then processed for microscopic examination. A number of minimally invasive techniques are available for retrieving and collecting cell samples from a patient, e.g., by using a fine needle aspiration biopsy, or by brushing body cavity surfaces accessible through minimally invasive endoscopic techniques. A variety of cell sample processing techniques are also known, such as the Cytospin® technique and the Thin-prep® technique, for depositing cellular materials and tissue fragments directly onto a microscope slide. Another technique, commonly referred to as a cell block preparation, immobilizes cellular materials and/or small tissue fragments within a solid support structure, typically paraffin. Thin sections of the cell block are then cut with a microtome and mounted onto a microscope slide for examination.
U.S. Pat. No. 6,913,921 (“the '921 patent”) discloses and describes methods and apparatus for cell block preparation, including providing a tissue collection cassette that serves a dual function of capturing cellular sample matter and providing a fluid pathway through which the cell processing and embedding reagents can flow. The cellular sample material is provided in an aqueous solution or a liquid cell preservative, which is passed through the tissue cassette across a filter that traps the cells and tissue fragments. A reagent flow pathway is configured to sequentially pass embedding reagents (alcohol, xylene, eosin stain) and liquefied paraffin through the tissue cassette and the cell sample already deposited on the filter. Once the paraffin is cooled, the filter is peeled away, leaving a paraffin “disk” protruding from the tissue cassette, with embedded cellular matter positioned at the end of the disk in a plane at which a tissue section can be cut using a standard microtome for microscope examination.
U.S. patent application Ser. No. 11/839,533, filed Aug. 15, 2007, and assigned to the assignee of the present invention (“the '533 application”), discloses a substantially automated cell block creation that does not require human oversight, including a two-piece cassette and filter assembly, to achieve more consistent cellular matter quantities in the created cell blocks, shorter processing time, reduced use of hazardous reagents, and more fully encapsulated cell blocks to preserve nucleic acid integrity. The contents of the '921 patent and '533 application are hereby fully incorporated by reference.
Upon completion of a cell block using the disclosed processes of the '921 patent and '533 application, a “re-melting” step is employed in order to transform the cell face shape from circular to square and more fully encapsulate the “cell spot” (the layer of cells collected cells from the cell block formation process), so that it may be processed on a standard microtome. In doing so, however, the (still circular) cell spot remains positioned at the “bottom” of the embedding mold, and outer surface of the cell block. However, many histologists would prefer to have an additional layer (volume) of wax between the end of the protruding wax block and the cell spot.